The field of the present invention is structures made of simple frame elements and flexible sheet material.
Structures which are composed of one or more continuous flexible figure eight loops with fabric extending between sections of the loops to define a partial or full enclosure have been developed which can be quickly erected or collapsed. Such devices are illustrated in U.S. Pat. No. 3,900,463; U.S. Pat. No. 4,825,892; and U.S. Pat. No. 5,038,812, the disclosures of each of which are incorporated herein by reference.
The simplest of the structures disclosed in the aforementioned patents is formed by a single figure eight frame. Structures using this frame construction have proven to be stable in the erected position. Even so, they remain quite flexible in keeping with their facile erectible and collapsible nature.
Other devices have used flexible figure eight loops. Collapsible automobile window shades employ a loop contained within a bag to create a planar shade. The loop, when expanded, stretches the bag to fill the window. To maintain the figure eight form, the portions of the loop at the cross over point are pinned together. As the natural tendency of the loop in this application is to be open, the pin allows free relative rotation of the loop portions for facile deployment. The pin is used to keeps the loop portions together at the cross over. This insures that the shade remains substantially planar and in position.
Sheet material, including netting, can be arranged over a portion or all of the frame to define rounded tent-like structures, supporting structures for targets and the like, or containers or other devices utilizing the space-defining frame and support characteristics. The sheet material has included formed pockets and tubes to retain the frame member or members. The shapes of the structures have been principally defined by the operative frame elements arranged in the substantially continuous complex curved structure defined by the arched figure eight as constrained by the formed sheet material.
The sheet material has been used to define tighter curves, flat portions, and the like by constraining the frame element or elements. The frame elements have been left without permanent deformations such as tight bends and abrupt angles. This use of unbent frame elements has been encouraged by the spring steel makeup of the elements and by the desire to achieve a compact coiled device in the collapsed configuration. Reliance for shape has also been placed on the springy nature of the frame. Constraining elements and retainers have not been employed beyond the tensioning of the sheet material itself as interfering with the simplicity of the structure.